Hydrothermal synthesis and crystal structure of a hybrid material based on [Co-4(phen)(8)(H2O)(2)(HPO3)(2)](4+) and a highly reduced polyoxoanion

An unusual composite hybrid material [Co-4 (phen)(8) (H2O)(2) (HPO3)(2)](H3O)(3) [PMo8VI V-4(IV) O-40 ((VO)-O-IV) 2] 1 (phen = 1,10-phenanthroline) has been hydrothermally synthesized from a mixture of NH4VO3, Na2MoO4.2H(2)O, CoCl2.6H(2)O, phen, H3PO3 and water. It was characterized by elemental analysis, IR, UV-vis, XPS, EPR, TG and single crystal X-ray diffraction. The title compound is constructed from the organic-inorganic hybrid [Co-4(phen)(8)(H2O)(2) (HPO3)(2)](4+) and highly reduced bi-capped pseudo-Keggin [(PMo8V4O40)-V-VI-O-IV ((VO)-O-IV)(2)](7-) polyoxoanions The structure exhibits an extended 2D network through hydrogen bonds among cations, anions and H2O, combining polyoxometalates with metal phosphonates for the first time.

Formation of a supported hybrid bilayer membrane on gold: A sterically enhanced hydrophobic effect

Adsorption of a monolayer of didecanoyl-L-alpha-phosphatidylcholine (DDPC) from dispersions of small unilamellar vesicles onto hydrophobic surfaces was investigated by mean of cyclic voltammetry and impedance spectroscopy. The hydrophobic surfaces were self-assembled monolayers of 2-mereapto-3-n-octylthiophene (MOT) on gold. One characteristic of the MOT monolayer is its permeability to organic molecules in aqueous solution, thus providing a more energetically favorable hydrophobic surface for the addition of phospholipid vesicles. The kinetics of the lipid monolayer formation were followed by measuring the time-dependent interfacial capacitance. Unusual values of thickness and capacitance of the MOT/ DDPC bilayers were observed. An interdigitating conformation of the bilayer structure was proposed to interpret the experimental results, The horseradish peroxidase reconstituted into the bilayer demonstrated the expected protein activity, showing practical use in research and in biosensor application.

Displacement and luminescence of Eu3+ in CaYBO4

CaY1-xBO4: xEu was synthesied by solid state reaction method, and the displacement and luminescence of the Eu3+ in CaYBO4 host were studied. Two luminescent centers could be observed at certain Eu3+-concentration, indicating that the Eu3+ occupies two different crystallographic sites. This result shows that the Eu3+ occupies two different Y3+ sites in CaYBO4. The investigation on Eu-O charge transfer bands indicates that the larger distortion or the lower symmetry of Eu3+ site is,the shorter wavelength of the Eu-O charge transfer band is. When the Eu3+-concentration is high (x > 0.10), Eu3+ occupies the sites of Ca2+ and is reduced to Eu2+.

Photosensitization of TiO2 nanoparticulate thin film electrodes by CdS nanoparticles

Surface photovoltage spectra (SPS) measurements of TiO2 show that a large surface state density is present on the TiO2 nanoparticles and these surface states can be efficiently decreased by sensitization using US nanoparticles as well as by suitable heat treatment. The photoelectrochemical behavior of the bare TiO2 thin film indicates that the mechanism of photoelectron transport is controlled by the trapping/detrapping properties of surface states within the thin films, The slow photocurrent response upon the illumination can be explained by the trap saturation effect. For a TiO2 nanoparticulate thin film sensitized using US nanoparticles, the slow photocurrent response disappears and the steady-state photocurrent increases drastically, which suggests that photosensitization can decrease the effect of surface states on photocurrent response.

Infrared spectra and VUV excitation properties of BaLnB(9)O(16): Re (Ln = La, Gd; Re = Eu, Tb)

The infrared spectra of BaLnB(9)O(16):Re, along with the VUV excitation spectra, have been measured. The spectra were tentatively interpreted in terms of the data on absorptions of the borate groups and band structure. It was observed that there are absorption due to BO3 and BO4 groups, indicating that there are BO3 and BO4 groups in BaLnB(9)O(16). It is found that absorption of the borate groups is located in the range from 120 to 170 mn. This result reveals that there is an energy transfer from host to the rare earth ions. It also observed that the energy of charge transfer band, the host absorption, the total crystal field splitting of d-levels of Tb3+ increase with the decrease in the Ln(3+) radius. (C) 2001 Elsevier Science B.V. All rights reserved.

Surface photovoltage spectra and photoelectrochemical properties of semiconductor-sensitized nanostructured TiO2 electrodes

Three kinds of TiO2 nanostructured thin films and their CdS-sensitized films, consisting of different sizes of TiO2 nanoparticles prepared with different methods, have been investigated. The surface photovoltage spectra (SPS) measurements indicate that the density of surface states on TiO2 is likely dependent upon the details of prepared methods. TiO2 particles prepared from basic sol have more surface states than that prepared from acidic sol. When the TiO2 thin films prepared using the TiO2 sols were sensitized by CdS particles, the SPS responses relative to the surface states on TiO2 from 350 to 800 nm were decreased. The photoelectrochemical properties of nanostructured TiO2 electrodes suggest that the fewer the surface states and the smaller the particle sizes of TiO2, the larger the photocurrent response. For CdS sensitized TiO2 thin film electrode, it is shown that the semiconductor sensitization is an efficient way to decrease the influence of surface states on the charge separation, and can improve the intensity of photocurrent response. (C) 2001 Elsevier Science B.V. All rights reserved.

Characterization of multilayer film using electrochemical impedance spectroscopy

A new multilayer film fabricated based on electrostatic attraction in this laboratory was firstly characterized by the electrochemical impedance spectroscopy. The relationship between the charge-transfer resistance and double-layer capacitance with the number of layers was obtained through analyzing the impedance data. It demonstrated that the multilayer film showed a unique structure with the film growth. Compared to other electrochemical methods, the electrochemical impedance spectroscopy was proved to be a very sensitive and useful technique for characterizing the multilayer films.

Amperometric determination of thiosulfate at a surface-renewable nickel(II) hexacyanoferrate-modified carbon ceramic electrode

Graphite powder-supported nickel(II) hexacyanoferrate (NiHCF) was prepared by the in situ chemical deposition method and then dispersed into methyltrimethoxysilane-derived gels to form a conductive composite. The composite was used as electrode material to construct a surface-renewable three-dimensional NiHCF-modified carbon ceramic electrode. Electrochemical behavior of the chemically modified electrode was well characterized using cyclic and square-wave voltammetry. The electrode presented a good electrocatalytic activity toward the oxidization of thiosulfate and thus was used as an amperometric sensor for thiosulfate in the photographic waste effluent. In addition, the electrode exhibited a distinct advantage of surface-renewal by simple mechanical polishing, as well as simple preparation, good chemical and mechanical stability. (C) 2001 Elsevier Science B.V. All rights reserved.

Formation and characterization of heteropolyacid/polycation multilayer films on gold electrode

Ultrathin multilayer films of a polybasic lanthanide heteropoly tungstate-molybdate complex and a cationic polymer of quaternized poly(4-vinylpyridine) partially complexed with osmium bis(2,2'-bipyridine) have been fabricated on a gold electrode precoated with a cysteamine self-assembled monolayer. The multilayer films have been characterized by optical spectroscopy, small-angle X-ray diffraction, and electrochemical methods (cyclic voltammetry and electrochemical impedance). Especially, the electrochemical impedance spectroscopy is developed to monitor the layer deposition processes. It provides important information such as double-layer capacitance and charge-transfer resistance. All obtained results reveal regular film growth with each layer adsorption. (C) 2001 The Electrochemical Society.

The luminescence of the phosphor Sr2ZrO4 with one-dimensional chains structure

A new type of phosphor Sr2ZrO4 with one-dimensional structure was prepared by solid reaction and its luminescence is seen at room temperature. The excitation and emission spectra were measured and display broad maximum at 354 nm and 386 nm respectively. The mechanism of this luminescence is ascribed to charge transfer.

Studies on the coordination of Pr(III) with adrenaline by potentiometry and absorption spectroscopy

The stability constant for complex of Pr(III) with adrenaline has been determined by potentiometric titration under biological conditions (37 degrees C and 0.15 mol/L NaCl). The absorption spectra of the Pr(III)-adrenaline system exhibit characteristic bands of Pr(III) at lower pH values. However, the charge transfer band which is due to the coordination of Pr(III) with adrenaline has been observed at higher pH values.

Fabrication and fluorescence study of sensitizing dye TiO2 films

Fluorescence spectra of the sensitizing dye/TiO2 bilayer films were studied. Charge-transfer complexes were formed in the above bilayer.

Synthesis, properties and crystal structure of organic-inorganic radical salt (DBTTF)(6)HPMo12O40 center dot 2H(2)O

Organic-inorganic radical salt (DBTTF)(6)PMo12O40 . 2H(2)O was synthesized by electrocrystallization and characterized by IR spectrum, electronic spectrum and ESR technology, Its magnetic property, conductivity and crystal structure were determined. The title compound crystallized in a triclinic system with P1 space group, a = 1.378 7(7), b = 1.420 4 (2), c = 1.570 2(2) nm, alpha = 104.57(1)degrees, beta = 103.41(2)degrees, gamma = 95.80(2)degrees, V = 2.853(2) nm(3) Z = 1 and a final R = 0.072 7.

Electrochemical quartz crystal microbalance study for vanadium hexacyanoferrates: monitoring of film growth and ion effects during redox reactions

An electrochemical quartz crystal microbalance was employed to monitor directly the growth of vanadium hexacyanoferrate (VHF) films on platinum substrates during electrodeposition and interfacial coagulation in the solution containing sulfuric acid electrolyte, vanadium(IV) and hexacyanoferrate(III). Mass changes of the gold/crystal working electrode were correlated with cyclic voltammetry data. Effects of cations (NH4+, Li+, Na+ and K+), anions (SO42- and NO3-) and solvent during redox reactions of the films were studied. The results show that cations were incorporated into the film during reduction and expelled from the film during oxidation. Solvent also participates in VHF electrochemistry, and its role cannot be neglected. Anions play no role in VHF electrochemistry. (C) 1997 Elsevier Science S.A.

The aggregation state of polyimide

The aggregation slate of polyimide in solution and in the solid state were studied using the NMR and fluorescence techniques. The experiment results show that the decay of spin-spin relaxation of polyimides with concentration can be described as a single exponential, biexponential, triexponential, biexponential profile. Meanwhile, the intensities of fluorencence spectra increase rapidly with the concentration, and some peaks have a red-shift. Based upon these experiment results, it can be concluded that polyimide in solution is very flexible, and there are several critical concentrations at which polyimide has distinctly different aggregation states. The existence of intermolecular charge transfer interaction between polyimide chains has been proved, and the interaction has a profound effect on the glass transition temperature, T-g, and the dynamic mechanical modulus of polyimide. (C) 1997 Elsevier Science Ltd.